1. Field of the Invention
This invention relates to a blood collection assembly including a microcollection container and a collector, and more particularly relates to an assembly pretreated to improve blood flow, platelet stability and clotting resistance.
2. Background of the Invention.
Recent advancements in analytical instrumentation have made it possible to carry out a variety of hematological or chemical diagnostic procedures on very small quantities of blood, such as may be obtained by puncture of a patient's finger, earlobe or an infant's heel. Accordingly, a variety of blood sample microcollection devices have been disclosed in the art.
In designing blood microcollection equipment, several important factors have long been recognized. First, microcollection procedures typically employ skin puncture to the finger of an adult or heel of an infant. The clotting process is naturally triggered in a wound such as this and the blood entering the tube is already clotting. The clotting chain reaction must be stopped urgently to prevent its completion. Second, it is well known in the art that blood flows poorly in small diameter plastic tubes, tends to hangup on the walls of the tube and is very difficult to mix with an anticoagulant added to the tube to delay clotting. Third, the plastic surface of the tube itself is generally poorly blood compatible and may initiate clotting. These factors contribute to decreased flow into the reservoir at the bottom of the tube.
To aid in blood flow, it has been conventional in the art to add a surfactant to the tube, for example as a coating or molding additive. In addition, anticoagulants have been used to discourage clotting. Surfactants, however, may interact with the collected blood specimen and interfere with the intended analytical procedure. For example, it is known that specimens taken for platelet counting, which must be continuously mixed to maintain homogeneity during counting, often suffer platelet loss during mixing on a mechanical tube mixer.
As a result, much effort has been expended to develop blood collection devices of improved flow characteristics which allow collection and mixing of samples without the use of chemical aids such as surfactants. In early work, a cap having an integral capillary tube for engaging the puncture and conducting the blood to the container was fitted to the top of the container. However, with such an arrangement, the tip of the capillary tube had to be arranged precisely adjacent the puncture wound and the entire apparatus had to be so positioned that the blood flow along the bottom surface of the tubular microcollection container was continuous in order to engage the surface of the container. Otherwise, if a precise positioning was not carried out, blood did not readily flow from capillary tube to the reservoir where the anticoagulant was contained. Representative such collectors are taught by Blecher et al. in U.S. Pat. No. 4,024,857.
An assembly disclosed in U.S. Pat. No. 4,397,318 to Burns includes a scoop collector which is connected to the microcollection container. The scoop provides a substantially larger surface for engaging the puncture and a substantially larger transfer surface for rapidly transferring the blood from the collector into the microcollection container. Because of the relatively large surface for engaging the puncture wound, the arrangement does not require a precise positioning of the scoop in order to initiate and rapidly transfer a quantity of blood to the microcollection container.
One problem with the scoop collector taught and claimed in U.S. Pat. No. 4,397,318, although the arrangement taught therein is highly efficient for the rapid collection of a blood sample into a microcollection container, is the fact that because of the very rapid collection of blood by the scoop collector, the separate blood passage in the collector becomes somewhat occluded by the blood passing therethrough and there is hang up on the walls thereof by capillary action.
U.S. Pat. No. 4,653,512 to Losada eliminates the blood passage caused by the separate vane or wall of the scoop collector of the '318 patent. The collector of the Losada invention has longitudinal ribs extending only part way into the combined blood/air passage. The ribs contain blood flow so that the blood does not touch the walls of the combined passage through the entire circumferential extent thereof. For this reason, capillary action causing blood hang-up does not take place and blood flows rapidly through the passage. This also reduces blood sample waste in the very small total quantities involved, resulting in a larger specimen yield. Moreover, such an arrangement reduces the need for incorporating expensive blood flow agents in the collector devices of the invention.
Nugent, in U.S. Pat. No. 4,646,753 discloses a scoop collector having a plurality of discontinuities in the distal end of the body portion which facilitate more rapid transfer of blood from the collector into a container and minimize the amount of blood which must be taken from the puncture wound in order to obtain a sufficient sample in the container.
In U.S. Pat. No. 4,690,153, Losada et al. discloses a plurality of separate or integral elongated members in the form of a rod or strip or a plurality of grooves which induce a continuous blood flow from the puncture to the final blood reservoir in the container.
While the above improvements have greatly advanced the art with respect to blood flow and minimization of blood hangup and clotting, there remains a need for further improvements, particularly with respect to the platelet stability. It is toward the goal of combining the rapid blood flow of chemically treated tubes with the platelet stability of untreated tubes that the present invention is directed.